The complexity of modern systems such as weapons, aircraft, ground transportation and the demands for their rapid development and qualification has resulted in the escalation of costs associated with their successful and timely introduction.
A revolutionary improvement in the cost and time of development of these systems could be realized if prototype models, scaled or full scale, of critical system components could be rapidly produced and subjected to proof testing.
Furthermore, the ability to conduct tests of these critical components early in their development would allow many more iterations of a design to be conducted in a short time, thus significantly improving the system's reliability, allowing early incorporation/evaluation of the system maintainability features, and significantly reducing the overall development time and cost.
There are three major 3-Dimensional model rapid prototyping methods currently available:
a. Photocurable liquid solidification or Stereolithography.
b. Selective Laser Sintering (SLS) or powder layer sintering.
c. Fused Deposition Modeling (FDM) or extruded molten plastic deposition method.
The above methods use geometric data from numerous currently available Computer Aided Design (CAD) solid modeling systems. This data is imported into a rapid prototyping system. A computer generated solid model is sliced into horizontal layers that are used as input for control of the rapid prototyping system.
Stereolithography is currently the most popular rapid prototyping method. Stereolithography generates a 3-D model by directing a laser beam onto the surface of a vat of liquid photocurable polymer. An elevator table in the polymer vat rests just below the liquid's surface. A laser beam is directed onto the polymer surface and solidifies it at the point of laser beam impingement. After a part slice at one depth has been made by scanning the laser beam back and forth in the shape of the model or pattern to be developed, the elevator platform upon which the model is being constructed drops the programmed amount. Another layer or slice is then created on top of the first in the same manner.
The process continues until the complete model has been constructed. After the construction phase is completed a curing process in a special curing apparatus is necessary.
The photocurable liquid plastics currently used in stereolithography are limited to acrylic plastics and produce parts with low strength and poor dimensional stability, especially during the transition through the curing process.
Selective Laser Sintering (SLS) generates a 3-D model by directing a laser beam onto a thin layer of plastic powder deposited on a target surface. The first layer corresponds to a first cross-sectional region of the part. The powder is sintered by operating the directed laser energy within the boundaries defining the first layer. A second layer of plastic powder is deposited on the first sintered layer, and the aim of the laser beam is scanned within the boundaries defining the second layer. Successive portions of powder are deposited onto the previously sintered layers until the complete model has been constructed.
A larger selection of plastic powder materials is used in this method. Plastics like PVC, Nylon, Polycarbonate and Wax are used. The part's quality and dimensional stability are sensitive to the powder moisture content and powder purity which strongly influence the laser beam energy absorption and powder sintering process. The parts produced by this method have poor dimensional stability and poor strength at relatively low temperatures.
Fused Deposition Modeling (FDM) generates a 3-D model by depositing extruded molten plastic in successive thin laminations in a pattern within the boundaries defining the part's layers. The material then solidifies as it is directed into place with an X-Y controlled extruding head nozzle that creates a thin laminate.
The thermoplastic melt temperature must be maintained within one degree Fahrenheit above the solidification point to secure proper adherence to the previous layer.
The materials used in the Fused Deposition Modeling method are limited to wax and plastic material with a melting temperature below 220 degrees Fahrenheit.
All of the above mentioned rapid prototyping methods are limited to applications for the prototype form evaluation or as a model used in further industrial processes, such as investment casting. The quality of these prototypes in terms of accuracy and dimensional stability is strongly dependent on particular qualities of the plastic materials used in the process and the process variations.
The accuracy of the 3-D models and their dimensional stability is also strongly dependent on process variations such as temperature of the processed plastic and its chemical purity and moisture content.
Those materials are limited to plastics with low melting temperatures and limited physical characteristics. The 3-D models produced with these rapid prototype methods have very poor strength, ductility and dimensional stability over time.
These material limitations make the previously existing methods unsuitable for producing prototype models which would have the materials of construction identical or close to the materials used in the final product. Therefore, the 3-D models produced on these systems are not suitable for model functional testing in the majority of cases.
A need exists for new and improved prototype modeling.